This application claims priority to an application entitled xe2x80x9cPREMISES OPTICAL CABLE WITH S-Z STRANDED STRENGTH MEMBER,xe2x80x9d filed in the Korean Industrial Property Office on Jan. 24, 2002 and assigned Serial No. 2002-4116, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an optical-fiber cable and, more particularly, to a premises-fiber optical cable.
2. Description of the Related Art
Premises-fiber optical cables are employed in a network for interconnecting telephone offices to each other and in a network for connecting telephone subscribers to a distribution cable. In general, the diameter of an optical fiber is substantially smaller than that of a conventional telephone cable, but the optical fiber has a wider bandwidth. However, the optical fiber can be easily damaged by a tension stress applied to the optical fiber in the longitudinal direction or by an external impact applied to the optical fiber in the diametric direction.
FIG. 1 is a cross-sectional view of a premises-fiber optical cable having a spirally-stranded strength member, and FIG. 2 is an exploded side view of the premises optical cable shown in FIG. 1. As shown, the optical cable comprises twelve tightly-coated optical fibers 110 and 130, strength members 120 and 140, a rip cord 150, and an outer jacket 160. The twelve tightly-coated optical fibers 110 and 130 include three inner-coated, optical fibers 110 and nine outer-coated optical fibers 130. The strength members 120 and 140 include an inner-strength member made of an inner yarn 120 and an outer-strength member made of an outer yarn 140.
Th above structure is disclosed in U.S. Pat. No. 4,781,433, entitled xe2x80x9cOptical Fiber Plenum Cable and Method of Making,xe2x80x9d in the names of Candido J. Arroyo, et al. Each of the inner and outer-coated optical fibers 110 and 130 comprises a core 132, a clad 134, and a tightly-coated layer 136. An exemplary inner-coated optical fiber 110 having an S-Z type stranded-lay configuration is disclosed in U.S. Pat. No. 4,828,352, entitled xe2x80x9cS-Z Stranded Optical Cable,xe2x80x9d in the name of Heinrich A. Kraft.
The inner yarn 120 surrounds the circumferences of the three inner-coated, optical fibers 110 and is spirally wound around the central member. The inner yarn 120 maintains a stranding condition of the inner-coated, optical fibers 110 and serves to buffer an external pressure applied to the optical fibers. The inner and outer yarns 120 and 140 may be made of aramid yarn. The nine, outer-coated optical fibers 130 are S-Z type stranded and surround the inner yarn 120 and the inner tightly-coated optical fibers 110. Similarly, the outer yarn 140 surrounds the circumferences of the nine, outer-coated optical fibers 130 and are spirally stranded. Together with the inner yarn 120, the outer yarn 140 serves to buffer the external pressure applied to the optical fibers. The outer jacket 160 is disposed at the outermost region of the optical cable and formed by extrusion. The outer jacket 160 may be made of a polymer such as Polyvinyl Chloride. The rip cord 150 is disposed adjacent to the inner wall of the outer jacket 160 to allow a worker to remove the outer jacket 160 easily.
Briefly, a method for manufacturing the conventional premises optical cable is as follows. First, the inner tightly-coated optical fibers 110 are S-Z type stranded. Second, the inner yarn 120 is spirally stranded. Third, the outer tightly-coated optical fibers 130 are S-Z type stranded. Fourth, the outer yarn 140 is spirally stranded. Fifth, the outer jacket 160 is formed by extrusion.
In the aforementioned conventional premises optical cable, the inner-coated optical fibers 110 and the outer-coated optical fibers 130 are S-Z type stranded about the central member, but the inner yarn 120, interposed between the inner and outer tightly-coated optical fibers 110 and 130, is spirally stranded. Therefore, in case a pressure from the outside is applied to the premises optical cable, the inner yarn 120 can not buffer the external pressure sufficiently. That is, in the section where the inner yarn 120 is stranded in the same direction of the stranding of the inner and outer-coated optical fibers 110 and 130, the inner yarn 120 is parallel to the inner and outer coated optical fibers 110 and 130, thus having a comparatively large area that is capable of buffering the external pressure. However, in the section where the inner yarn 120 is stranded in the opposite direction of the stranding of the inner and outer-coated optical fibers 110 and 130, the inner yarn 120 is stranded in a crosswise direction to the inner and outer-coated optical fibers 110 and 130, thereby having a comparatively smaller area capable of buffering the external pressure. Therefore, due to the lack of the uniformity of the buffered area, the inner yarn 120 can not achieve a sufficient buffering function.
Therefore, the present invention has been made in view of the above problems and provides additional advantages by providing premises-fiber optical cables with an improved buffering function.
In accordance with the present invention, the premises optical cable with a S-Z stranded strength member includes: a plurality of tightly-coated inner optical fibers disposed at the central region of the optical cable and being S-Z type stranded; a plurality of inner yarns S-Z type stranded for surrounding the inner tightly-coated optical fibers; a plurality of tightly-coated outer optical fibers S-Z type stranded for surrounding the circumference of the tightly coated inner optical fibers; a plurality of outer yarns spirally stranded for surrounding the tightly-coated outer optical fibers; and, an outer jacket disposed at the outermost region of the optical cable for surrounding the outer yarns.